/**
 * @file
 * User Datagram Protocol module\n
 * The code for the User Datagram Protocol UDP & UDPLite (RFC 3828).\n
 * See also @ref udp_raw
 *
 * @defgroup udp_raw UDP
 * @ingroup callbackstyle_api
 * User Datagram Protocol module\n
 * @see @ref api
 */

/*
 * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without modification,
 * are permitted provided that the following conditions are met:
 *
 * 1. Redistributions of source code must retain the above copyright notice,
 *    this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright notice,
 *    this list of conditions and the following disclaimer in the documentation
 *    and/or other materials provided with the distribution.
 * 3. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
 * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
 * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
 * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
 * OF SUCH DAMAGE.
 *
 * This file is part of the lwIP TCP/IP stack.
 *
 * Author: Adam Dunkels <adam@sics.se>
 *
 */

/* @todo Check the use of '(struct udp_pcb).chksum_len_rx'!
 */

#include "lwip/opt.h"

#if LWIP_UDP /* don't build if not configured for use in lwipopts.h */

#include "lwip/udp.h"
#include "lwip/def.h"
#include "lwip/memp.h"
#include "lwip/inet_chksum.h"
#include "lwip/ip_addr.h"
#include "lwip/ip6.h"
#include "lwip/ip6_addr.h"
#include "lwip/netif.h"
#include "lwip/icmp.h"
#include "lwip/icmp6.h"
#include "lwip/stats.h"
#include "lwip/snmp.h"
#include "lwip/dhcp.h"

#include <string.h>

#ifdef LWIP_HOOK_FILENAME
#include LWIP_HOOK_FILENAME
#endif

#ifndef UDP_LOCAL_PORT_RANGE_START
/* From http://www.iana.org/assignments/port-numbers:
   "The Dynamic and/or Private Ports are those from 49152 through 65535" */
#define UDP_LOCAL_PORT_RANGE_START 0xc000
#define UDP_LOCAL_PORT_RANGE_END   0xffff
#define UDP_ENSURE_LOCAL_PORT_RANGE(port) \
    ((u16_t)(((port) & (u16_t)~UDP_LOCAL_PORT_RANGE_START) + UDP_LOCAL_PORT_RANGE_START))
#endif

/* last local UDP port */
static u16_t udp_port = UDP_LOCAL_PORT_RANGE_START;

/* The list of UDP PCBs */
/* exported in udp.h (was static) */
struct udp_pcb* udp_pcbs;

/**
 * Initialize this module.
 */
void udp_init(void)
{
#ifdef LWIP_RAND
    udp_port = UDP_ENSURE_LOCAL_PORT_RANGE(LWIP_RAND());
#endif /* LWIP_RAND */
}

/**
 * Allocate a new local UDP port.
 *
 * @return a new (free) local UDP port number
 */
static u16_t udp_new_port(void)
{
    u16_t n = 0;
    struct udp_pcb* pcb;

again:
    if (udp_port++ == UDP_LOCAL_PORT_RANGE_END)
    {
        udp_port = UDP_LOCAL_PORT_RANGE_START;
    }
    /* Check all PCBs. */
    for (pcb = udp_pcbs; pcb != NULL; pcb = pcb->next)
    {
        if (pcb->local_port == udp_port)
        {
            if (++n > (UDP_LOCAL_PORT_RANGE_END - UDP_LOCAL_PORT_RANGE_START))
            {
                return 0;
            }
            goto again;
        }
    }
    return udp_port;
}

/** Common code to see if the current input packet matches the pcb
 * (current input packet is accessed via ip(4/6)_current_* macros)
 *
 * @param pcb pcb to check
 * @param inp network interface on which the datagram was received (only used for IPv4)
 * @param broadcast 1 if his is an IPv4 broadcast (global or subnet-only), 0 otherwise (only used for IPv4)
 * @return 1 on match, 0 otherwise
 */
static u8_t udp_input_local_match(struct udp_pcb* pcb, struct netif* inp, u8_t broadcast)
{
    LWIP_UNUSED_ARG(inp);       /* in IPv6 only case */
    LWIP_UNUSED_ARG(broadcast); /* in IPv6 only case */

    LWIP_ASSERT("udp_input_local_match: invalid pcb", pcb != NULL);
    LWIP_ASSERT("udp_input_local_match: invalid netif", inp != NULL);

    /* check if PCB is bound to specific netif */
    if ((pcb->netif_idx != NETIF_NO_INDEX) && (pcb->netif_idx != netif_get_index(ip_data.current_input_netif)))
    {
        return 0;
    }

    /* Dual-stack: PCBs listening to any IP type also listen to any IP address */
    if (IP_IS_ANY_TYPE_VAL(pcb->local_ip))
    {
#if LWIP_IPV4 && IP_SOF_BROADCAST_RECV
        if ((broadcast != 0) && !ip_get_option(pcb, SOF_BROADCAST))
        {
            return 0;
        }
#endif /* LWIP_IPV4 && IP_SOF_BROADCAST_RECV */
        return 1;
    }

    /* Only need to check PCB if incoming IP version matches PCB IP version */
    if (IP_ADDR_PCB_VERSION_MATCH_EXACT(pcb, ip_current_dest_addr()))
    {
#if LWIP_IPV4
        /* Special case: IPv4 broadcast: all or broadcasts in my subnet
         * Note: broadcast variable can only be 1 if it is an IPv4 broadcast */
        if (broadcast != 0)
        {
#if IP_SOF_BROADCAST_RECV
            if (ip_get_option(pcb, SOF_BROADCAST))
#endif /* IP_SOF_BROADCAST_RECV */
            {
                if (ip4_addr_isany(ip_2_ip4(&pcb->local_ip)) || ((ip4_current_dest_addr()->addr == IPADDR_BROADCAST))
                    || ip4_addr_netcmp(ip_2_ip4(&pcb->local_ip), ip4_current_dest_addr(), netif_ip4_netmask(inp)))
                {
                    return 1;
                }
            }
        }
        else
#endif /* LWIP_IPV4 */
            /* Handle IPv4 and IPv6: all or exact match */
            if (ip_addr_isany(&pcb->local_ip) || ip_addr_cmp(&pcb->local_ip, ip_current_dest_addr()))
            {
                return 1;
            }
    }

    return 0;
}

/**
 * Process an incoming UDP datagram.
 *
 * Given an incoming UDP datagram (as a chain of pbufs) this function
 * finds a corresponding UDP PCB and hands over the pbuf to the pcbs
 * recv function. If no pcb is found or the datagram is incorrect, the
 * pbuf is freed.
 *
 * @param p pbuf to be demultiplexed to a UDP PCB (p->payload pointing to the UDP header)
 * @param inp network interface on which the datagram was received.
 *
 */
void udp_input(struct pbuf* p, struct netif* inp)
{
    struct udp_hdr* udphdr;
    struct udp_pcb *pcb, *prev;
    struct udp_pcb* uncon_pcb;
    u16_t src, dest;
    u8_t broadcast;
    u8_t for_us = 0;

    LWIP_UNUSED_ARG(inp);

    LWIP_ASSERT_CORE_LOCKED();

    LWIP_ASSERT("udp_input: invalid pbuf", p != NULL);
    LWIP_ASSERT("udp_input: invalid netif", inp != NULL);

    PERF_START;

    UDP_STATS_INC(udp.recv);

    /* Check minimum length (UDP header) */
    if (p->len < UDP_HLEN)
    {
        /* drop short packets */
        LWIP_DEBUGF(UDP_DEBUG, ("udp_input: short UDP datagram (%" U16_F " bytes) discarded\n", p->tot_len));
        UDP_STATS_INC(udp.lenerr);
        UDP_STATS_INC(udp.drop);
        MIB2_STATS_INC(mib2.udpinerrors);
        pbuf_free(p);
        goto end;
    }

    udphdr = (struct udp_hdr*)p->payload;

    /* is broadcast packet ? */
    broadcast = ip_addr_isbroadcast(ip_current_dest_addr(), ip_current_netif());

    LWIP_DEBUGF(UDP_DEBUG, ("udp_input: received datagram of length %" U16_F "\n", p->tot_len));

    /* convert src and dest ports to host byte order */
    src = lwip_ntohs(udphdr->src);
    dest = lwip_ntohs(udphdr->dest);

    udp_debug_print(udphdr);

    /* print the UDP source and destination */
    LWIP_DEBUGF(UDP_DEBUG, ("udp ("));
    ip_addr_debug_print_val(UDP_DEBUG, *ip_current_dest_addr());
    LWIP_DEBUGF(UDP_DEBUG, (", %" U16_F ") <-- (", lwip_ntohs(udphdr->dest)));
    ip_addr_debug_print_val(UDP_DEBUG, *ip_current_src_addr());
    LWIP_DEBUGF(UDP_DEBUG, (", %" U16_F ")\n", lwip_ntohs(udphdr->src)));

    pcb = NULL;
    prev = NULL;
    uncon_pcb = NULL;
    /* Iterate through the UDP pcb list for a matching pcb.
     * 'Perfect match' pcbs (connected to the remote port & ip address) are
     * preferred. If no perfect match is found, the first unconnected pcb that
     * matches the local port and ip address gets the datagram. */
    for (pcb = udp_pcbs; pcb != NULL; pcb = pcb->next)
    {
        /* print the PCB local and remote address */
        LWIP_DEBUGF(UDP_DEBUG, ("pcb ("));
        ip_addr_debug_print_val(UDP_DEBUG, pcb->local_ip);
        LWIP_DEBUGF(UDP_DEBUG, (", %" U16_F ") <-- (", pcb->local_port));
        ip_addr_debug_print_val(UDP_DEBUG, pcb->remote_ip);
        LWIP_DEBUGF(UDP_DEBUG, (", %" U16_F ")\n", pcb->remote_port));

        /* compare PCB local addr+port to UDP destination addr+port */
        if ((pcb->local_port == dest) && (udp_input_local_match(pcb, inp, broadcast) != 0))
        {
            if ((pcb->flags & UDP_FLAGS_CONNECTED) == 0)
            {
                if (uncon_pcb == NULL)
                {
                    /* the first unconnected matching PCB */
                    uncon_pcb = pcb;
#if LWIP_IPV4
                }
                else if (broadcast && ip4_current_dest_addr()->addr == IPADDR_BROADCAST)
                {
                    /* global broadcast address (only valid for IPv4; match was checked before) */
                    if (!IP_IS_V4_VAL(uncon_pcb->local_ip)
                        || !ip4_addr_cmp(ip_2_ip4(&uncon_pcb->local_ip), netif_ip4_addr(inp)))
                    {
                        /* uncon_pcb does not match the input netif, check this pcb */
                        if (IP_IS_V4_VAL(pcb->local_ip) && ip4_addr_cmp(ip_2_ip4(&pcb->local_ip), netif_ip4_addr(inp)))
                        {
                            /* better match */
                            uncon_pcb = pcb;
                        }
                    }
#endif /* LWIP_IPV4 */
                }
#if SO_REUSE
                else if (!ip_addr_isany(&pcb->local_ip))
                {
                    /* prefer specific IPs over catch-all */
                    uncon_pcb = pcb;
                }
#endif /* SO_REUSE */
            }

            /* compare PCB remote addr+port to UDP source addr+port */
            if ((pcb->remote_port == src)
                && (ip_addr_isany_val(pcb->remote_ip) || ip_addr_cmp(&pcb->remote_ip, ip_current_src_addr())))
            {
                /* the first fully matching PCB */
                if (prev != NULL)
                {
                    /* move the pcb to the front of udp_pcbs so that is
                       found faster next time */
                    prev->next = pcb->next;
                    pcb->next = udp_pcbs;
                    udp_pcbs = pcb;
                }
                else
                {
                    UDP_STATS_INC(udp.cachehit);
                }
                break;
            }
        }

        prev = pcb;
    }
    /* no fully matching pcb found? then look for an unconnected pcb */
    if (pcb == NULL)
    {
        pcb = uncon_pcb;
    }

    /* Check checksum if this is a match or if it was directed at us. */
    if (pcb != NULL)
    {
        for_us = 1;
    }
    else
    {
#if LWIP_IPV6
        if (ip_current_is_v6())
        {
            for_us = netif_get_ip6_addr_match(inp, ip6_current_dest_addr()) >= 0;
        }
#endif /* LWIP_IPV6 */
#if LWIP_IPV4
        if (!ip_current_is_v6())
        {
            for_us = ip4_addr_cmp(netif_ip4_addr(inp), ip4_current_dest_addr());
        }
#endif /* LWIP_IPV4 */
    }

    if (for_us)
    {
        LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, ("udp_input: calculating checksum\n"));
#if CHECKSUM_CHECK_UDP
        IF__NETIF_CHECKSUM_ENABLED(inp, NETIF_CHECKSUM_CHECK_UDP)
        {
#if LWIP_UDPLITE
            if (ip_current_header_proto() == IP_PROTO_UDPLITE)
            {
                /* Do the UDP Lite checksum */
                u16_t chklen = lwip_ntohs(udphdr->len);
                if (chklen < sizeof(struct udp_hdr))
                {
                    if (chklen == 0)
                    {
                        /* For UDP-Lite, checksum length of 0 means checksum
                           over the complete packet (See RFC 3828 chap. 3.1) */
                        chklen = p->tot_len;
                    }
                    else
                    {
                        /* At least the UDP-Lite header must be covered by the
                           checksum! (Again, see RFC 3828 chap. 3.1) */
                        goto chkerr;
                    }
                }
                if (ip_chksum_pseudo_partial(
                        p,
                        IP_PROTO_UDPLITE,
                        p->tot_len,
                        chklen,
                        ip_current_src_addr(),
                        ip_current_dest_addr())
                    != 0)
                {
                    goto chkerr;
                }
            }
            else
#endif /* LWIP_UDPLITE */
            {
                if (udphdr->chksum != 0)
                {
                    if (ip_chksum_pseudo(p, IP_PROTO_UDP, p->tot_len, ip_current_src_addr(), ip_current_dest_addr())
                        != 0)
                    {
                        goto chkerr;
                    }
                }
            }
        }
#endif /* CHECKSUM_CHECK_UDP */
        if (pbuf_remove_header(p, UDP_HLEN))
        {
            /* Can we cope with this failing? Just assert for now */
            LWIP_ASSERT("pbuf_remove_header failed\n", 0);
            UDP_STATS_INC(udp.drop);
            MIB2_STATS_INC(mib2.udpinerrors);
            pbuf_free(p);
            goto end;
        }

        if (pcb != NULL)
        {
            MIB2_STATS_INC(mib2.udpindatagrams);
#if SO_REUSE && SO_REUSE_RXTOALL
            if (ip_get_option(pcb, SOF_REUSEADDR) && (broadcast || ip_addr_ismulticast(ip_current_dest_addr())))
            {
                /* pass broadcast- or multicast packets to all multicast pcbs
                   if SOF_REUSEADDR is set on the first match */
                struct udp_pcb* mpcb;
                for (mpcb = udp_pcbs; mpcb != NULL; mpcb = mpcb->next)
                {
                    if (mpcb != pcb)
                    {
                        /* compare PCB local addr+port to UDP destination addr+port */
                        if ((mpcb->local_port == dest) && (udp_input_local_match(mpcb, inp, broadcast) != 0))
                        {
                            /* pass a copy of the packet to all local matches */
                            if (mpcb->recv != NULL)
                            {
                                struct pbuf* q;
                                q = pbuf_clone(PBUF_RAW, PBUF_POOL, p);
                                if (q != NULL)
                                {
                                    mpcb->recv(mpcb->recv_arg, mpcb, q, ip_current_src_addr(), src);
                                }
                            }
                        }
                    }
                }
            }
#endif /* SO_REUSE && SO_REUSE_RXTOALL */
            /* callback */
            if (pcb->recv != NULL)
            {
                /* now the recv function is responsible for freeing p */
                pcb->recv(pcb->recv_arg, pcb, p, ip_current_src_addr(), src);
            }
            else
            {
                /* no recv function registered? then we have to free the pbuf! */
                pbuf_free(p);
                goto end;
            }
        }
        else
        {
            LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, ("udp_input: not for us.\n"));

#if LWIP_ICMP || LWIP_ICMP6
            /* No match was found, send ICMP destination port unreachable unless
               destination address was broadcast/multicast. */
            if (!broadcast && !ip_addr_ismulticast(ip_current_dest_addr()))
            {
                /* move payload pointer back to ip header */
                pbuf_header_force(p, (s16_t)(ip_current_header_tot_len() + UDP_HLEN));
                icmp_port_unreach(ip_current_is_v6(), p);
            }
#endif /* LWIP_ICMP || LWIP_ICMP6 */
            UDP_STATS_INC(udp.proterr);
            UDP_STATS_INC(udp.drop);
            MIB2_STATS_INC(mib2.udpnoports);
            pbuf_free(p);
        }
    }
    else
    {
        pbuf_free(p);
    }
end:
    PERF_STOP("udp_input");
    return;
#if CHECKSUM_CHECK_UDP
chkerr:
    LWIP_DEBUGF(
        UDP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
        ("udp_input: UDP (or UDP Lite) datagram discarded due to failing checksum\n"));
    UDP_STATS_INC(udp.chkerr);
    UDP_STATS_INC(udp.drop);
    MIB2_STATS_INC(mib2.udpinerrors);
    pbuf_free(p);
    PERF_STOP("udp_input");
#endif /* CHECKSUM_CHECK_UDP */
}

/**
 * @ingroup udp_raw
 * Sends the pbuf p using UDP. The pbuf is not deallocated.
 *
 *
 * @param pcb UDP PCB used to send the data.
 * @param p chain of pbuf's to be sent.
 *
 * The datagram will be sent to the current remote_ip & remote_port
 * stored in pcb. If the pcb is not bound to a port, it will
 * automatically be bound to a random port.
 *
 * @return lwIP error code.
 * - ERR_OK. Successful. No error occurred.
 * - ERR_MEM. Out of memory.
 * - ERR_RTE. Could not find route to destination address.
 * - ERR_VAL. No PCB or PCB is dual-stack
 * - More errors could be returned by lower protocol layers.
 *
 * @see udp_disconnect() udp_sendto()
 */
err_t udp_send(struct udp_pcb* pcb, struct pbuf* p)
{
    LWIP_ERROR("udp_send: invalid pcb", pcb != NULL, return ERR_ARG);
    LWIP_ERROR("udp_send: invalid pbuf", p != NULL, return ERR_ARG);

    if (IP_IS_ANY_TYPE_VAL(pcb->remote_ip))
    {
        return ERR_VAL;
    }

    /* send to the packet using remote ip and port stored in the pcb */
    return udp_sendto(pcb, p, &pcb->remote_ip, pcb->remote_port);
}

#if LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP
/** @ingroup udp_raw
 * Same as udp_send() but with checksum
 */
err_t udp_send_chksum(struct udp_pcb* pcb, struct pbuf* p, u8_t have_chksum, u16_t chksum)
{
    LWIP_ERROR("udp_send_chksum: invalid pcb", pcb != NULL, return ERR_ARG);
    LWIP_ERROR("udp_send_chksum: invalid pbuf", p != NULL, return ERR_ARG);

    if (IP_IS_ANY_TYPE_VAL(pcb->remote_ip))
    {
        return ERR_VAL;
    }

    /* send to the packet using remote ip and port stored in the pcb */
    return udp_sendto_chksum(pcb, p, &pcb->remote_ip, pcb->remote_port, have_chksum, chksum);
}
#endif /* LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP */

/**
 * @ingroup udp_raw
 * Send data to a specified address using UDP.
 *
 * @param pcb UDP PCB used to send the data.
 * @param p chain of pbuf's to be sent.
 * @param dst_ip Destination IP address.
 * @param dst_port Destination UDP port.
 *
 * dst_ip & dst_port are expected to be in the same byte order as in the pcb.
 *
 * If the PCB already has a remote address association, it will
 * be restored after the data is sent.
 *
 * @return lwIP error code (@see udp_send for possible error codes)
 *
 * @see udp_disconnect() udp_send()
 */
err_t udp_sendto(struct udp_pcb* pcb, struct pbuf* p, const ip_addr_t* dst_ip, u16_t dst_port)
{
#if LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP
    return udp_sendto_chksum(pcb, p, dst_ip, dst_port, 0, 0);
}

/** @ingroup udp_raw
 * Same as udp_sendto(), but with checksum */
err_t udp_sendto_chksum(
    struct udp_pcb* pcb,
    struct pbuf* p,
    const ip_addr_t* dst_ip,
    u16_t dst_port,
    u8_t have_chksum,
    u16_t chksum)
{
#endif /* LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP */
    struct netif* netif;

    LWIP_ERROR("udp_sendto: invalid pcb", pcb != NULL, return ERR_ARG);
    LWIP_ERROR("udp_sendto: invalid pbuf", p != NULL, return ERR_ARG);
    LWIP_ERROR("udp_sendto: invalid dst_ip", dst_ip != NULL, return ERR_ARG);

    if (!IP_ADDR_PCB_VERSION_MATCH(pcb, dst_ip))
    {
        return ERR_VAL;
    }

    LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, ("udp_send\n"));

    if (pcb->netif_idx != NETIF_NO_INDEX)
    {
        netif = netif_get_by_index(pcb->netif_idx);
    }
    else
    {
#if LWIP_MULTICAST_TX_OPTIONS
        netif = NULL;
        if (ip_addr_ismulticast(dst_ip))
        {
            /* For IPv6, the interface to use for packets with a multicast destination
             * is specified using an interface index. The same approach may be used for
             * IPv4 as well, in which case it overrides the IPv4 multicast override
             * address below. Here we have to look up the netif by going through the
             * list, but by doing so we skip a route lookup. If the interface index has
             * gone stale, we fall through and do the regular route lookup after all. */
            if (pcb->mcast_ifindex != NETIF_NO_INDEX)
            {
                netif = netif_get_by_index(pcb->mcast_ifindex);
            }
#if LWIP_IPV4
            else
#if LWIP_IPV6
                if (IP_IS_V4(dst_ip))
#endif /* LWIP_IPV6 */
            {
                /* IPv4 does not use source-based routing by default, so we use an
                   administratively selected interface for multicast by default.
                   However, this can be overridden by setting an interface address
                   in pcb->mcast_ip4 that is used for routing. If this routing lookup
                   fails, we try regular routing as though no override was set. */
                if (!ip4_addr_isany_val(pcb->mcast_ip4) && !ip4_addr_cmp(&pcb->mcast_ip4, IP4_ADDR_BROADCAST))
                {
                    netif = ip4_route_src(ip_2_ip4(&pcb->local_ip), &pcb->mcast_ip4);
                }
            }
#endif /* LWIP_IPV4 */
        }

        if (netif == NULL)
#endif /* LWIP_MULTICAST_TX_OPTIONS */
        {
            /* find the outgoing network interface for this packet */
            netif = ip_route(&pcb->local_ip, dst_ip);
        }
    }

    /* no outgoing network interface could be found? */
    if (netif == NULL)
    {
        LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, ("udp_send: No route to "));
        ip_addr_debug_print(UDP_DEBUG | LWIP_DBG_LEVEL_SERIOUS, dst_ip);
        LWIP_DEBUGF(UDP_DEBUG, ("\n"));
        UDP_STATS_INC(udp.rterr);
        return ERR_RTE;
    }
#if LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP
    return udp_sendto_if_chksum(pcb, p, dst_ip, dst_port, netif, have_chksum, chksum);
#else  /* LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP */
    return udp_sendto_if(pcb, p, dst_ip, dst_port, netif);
#endif /* LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP */
}

/**
 * @ingroup udp_raw
 * Send data to a specified address using UDP.
 * The netif used for sending can be specified.
 *
 * This function exists mainly for DHCP, to be able to send UDP packets
 * on a netif that is still down.
 *
 * @param pcb UDP PCB used to send the data.
 * @param p chain of pbuf's to be sent.
 * @param dst_ip Destination IP address.
 * @param dst_port Destination UDP port.
 * @param netif the netif used for sending.
 *
 * dst_ip & dst_port are expected to be in the same byte order as in the pcb.
 *
 * @return lwIP error code (@see udp_send for possible error codes)
 *
 * @see udp_disconnect() udp_send()
 */
err_t udp_sendto_if(struct udp_pcb* pcb, struct pbuf* p, const ip_addr_t* dst_ip, u16_t dst_port, struct netif* netif)
{
#if LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP
    return udp_sendto_if_chksum(pcb, p, dst_ip, dst_port, netif, 0, 0);
}

/** Same as udp_sendto_if(), but with checksum */
err_t udp_sendto_if_chksum(
    struct udp_pcb* pcb,
    struct pbuf* p,
    const ip_addr_t* dst_ip,
    u16_t dst_port,
    struct netif* netif,
    u8_t have_chksum,
    u16_t chksum)
{
#endif /* LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP */
    const ip_addr_t* src_ip;

    LWIP_ERROR("udp_sendto_if: invalid pcb", pcb != NULL, return ERR_ARG);
    LWIP_ERROR("udp_sendto_if: invalid pbuf", p != NULL, return ERR_ARG);
    LWIP_ERROR("udp_sendto_if: invalid dst_ip", dst_ip != NULL, return ERR_ARG);
    LWIP_ERROR("udp_sendto_if: invalid netif", netif != NULL, return ERR_ARG);

    if (!IP_ADDR_PCB_VERSION_MATCH(pcb, dst_ip))
    {
        return ERR_VAL;
    }

    /* PCB local address is IP_ANY_ADDR or multicast? */
#if LWIP_IPV6
    if (IP_IS_V6(dst_ip))
    {
        if (ip6_addr_isany(ip_2_ip6(&pcb->local_ip)) || ip6_addr_ismulticast(ip_2_ip6(&pcb->local_ip)))
        {
            src_ip = ip6_select_source_address(netif, ip_2_ip6(dst_ip));
            if (src_ip == NULL)
            {
                /* No suitable source address was found. */
                return ERR_RTE;
            }
        }
        else
        {
            /* use UDP PCB local IPv6 address as source address, if still valid. */
            if (netif_get_ip6_addr_match(netif, ip_2_ip6(&pcb->local_ip)) < 0)
            {
                /* Address isn't valid anymore. */
                return ERR_RTE;
            }
            src_ip = &pcb->local_ip;
        }
    }
#endif /* LWIP_IPV6 */
#if LWIP_IPV4 && LWIP_IPV6
    else
#endif /* LWIP_IPV4 && LWIP_IPV6 */
#if LWIP_IPV4
        if (ip4_addr_isany(ip_2_ip4(&pcb->local_ip)) || ip4_addr_ismulticast(ip_2_ip4(&pcb->local_ip)))
    {
        /* if the local_ip is any or multicast
         * use the outgoing network interface IP address as source address */
        src_ip = netif_ip_addr4(netif);
    }
    else
    {
        /* check if UDP PCB local IP address is correct
         * this could be an old address if netif->ip_addr has changed */
#if defined(LWIP_HOOK_UDP_TRANSMIT_LOCALIP_CMP)
        if (!LWIP_HOOK_UDP_TRANSMIT_LOCALIP_CMP(&(pcb->local_ip), netif))
        {
#else  /* !defined(LWIP_HOOK_UDP_TRANSMIT_LOCALIP_CMP) */
        if (!ip4_addr_cmp(ip_2_ip4(&(pcb->local_ip)), netif_ip4_addr(netif)))
        {
#endif /* defined(LWIP_HOOK_UDP_TRANSMIT_LOCALIP_CMP) */

            /* local_ip doesn't match, drop the packet */
            return ERR_RTE;
        }
        /* use UDP PCB local IP address as source address */
        src_ip = &pcb->local_ip;
    }
#endif /* LWIP_IPV4 */
#if LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP
    return udp_sendto_if_src_chksum(pcb, p, dst_ip, dst_port, netif, have_chksum, chksum, src_ip);
#else  /* LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP */
    return udp_sendto_if_src(pcb, p, dst_ip, dst_port, netif, src_ip);
#endif /* LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP */
}

/** @ingroup udp_raw
 * Same as @ref udp_sendto_if, but with source address */
err_t udp_sendto_if_src(
    struct udp_pcb* pcb,
    struct pbuf* p,
    const ip_addr_t* dst_ip,
    u16_t dst_port,
    struct netif* netif,
    const ip_addr_t* src_ip)
{
#if LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP
    return udp_sendto_if_src_chksum(pcb, p, dst_ip, dst_port, netif, 0, 0, src_ip);
}

/** Same as udp_sendto_if_src(), but with checksum */
err_t udp_sendto_if_src_chksum(
    struct udp_pcb* pcb,
    struct pbuf* p,
    const ip_addr_t* dst_ip,
    u16_t dst_port,
    struct netif* netif,
    u8_t have_chksum,
    u16_t chksum,
    const ip_addr_t* src_ip)
{
#endif /* LWIP_CHECKSUM_ON_COPY && CHECKSUM_GEN_UDP */
    struct udp_hdr* udphdr;
    err_t err;
    struct pbuf* q; /* q will be sent down the stack */
    u8_t ip_proto;
    u8_t ttl;

    LWIP_ASSERT_CORE_LOCKED();

    LWIP_ERROR("udp_sendto_if_src: invalid pcb", pcb != NULL, return ERR_ARG);
    LWIP_ERROR("udp_sendto_if_src: invalid pbuf", p != NULL, return ERR_ARG);
    LWIP_ERROR("udp_sendto_if_src: invalid dst_ip", dst_ip != NULL, return ERR_ARG);
    LWIP_ERROR("udp_sendto_if_src: invalid src_ip", src_ip != NULL, return ERR_ARG);
    LWIP_ERROR("udp_sendto_if_src: invalid netif", netif != NULL, return ERR_ARG);

    if (!IP_ADDR_PCB_VERSION_MATCH(pcb, src_ip) || !IP_ADDR_PCB_VERSION_MATCH(pcb, dst_ip))
    {
        return ERR_VAL;
    }

#if LWIP_IPV4 && IP_SOF_BROADCAST
    /* broadcast filter? */
    if (!ip_get_option(pcb, SOF_BROADCAST) &&
#if LWIP_IPV6
        IP_IS_V4(dst_ip) &&
#endif /* LWIP_IPV6 */
        ip_addr_isbroadcast(dst_ip, netif))
    {
        LWIP_DEBUGF(
            UDP_DEBUG | LWIP_DBG_LEVEL_SERIOUS,
            ("udp_sendto_if: SOF_BROADCAST not enabled on pcb %p\n", (void*)pcb));
        return ERR_VAL;
    }
#endif /* LWIP_IPV4 && IP_SOF_BROADCAST */

    /* if the PCB is not yet bound to a port, bind it here */
    if (pcb->local_port == 0)
    {
        LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, ("udp_send: not yet bound to a port, binding now\n"));
        err = udp_bind(pcb, &pcb->local_ip, pcb->local_port);
        if (err != ERR_OK)
        {
            LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("udp_send: forced port bind failed\n"));
            return err;
        }
    }

    /* packet too large to add a UDP header without causing an overflow? */
    if ((u16_t)(p->tot_len + UDP_HLEN) < p->tot_len)
    {
        return ERR_MEM;
    }
    /* not enough space to add an UDP header to first pbuf in given p chain? */
    if (pbuf_add_header(p, UDP_HLEN))
    {
        /* allocate header in a separate new pbuf */
        q = pbuf_alloc(PBUF_IP, UDP_HLEN, PBUF_RAM);
        /* new header pbuf could not be allocated? */
        if (q == NULL)
        {
            LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_LEVEL_SERIOUS, ("udp_send: could not allocate header\n"));
            return ERR_MEM;
        }
        if (p->tot_len != 0)
        {
            /* chain header q in front of given pbuf p (only if p contains data) */
            pbuf_chain(q, p);
        }
        /* first pbuf q points to header pbuf */
        LWIP_DEBUGF(UDP_DEBUG, ("udp_send: added header pbuf %p before given pbuf %p\n", (void*)q, (void*)p));
    }
    else
    {
        /* adding space for header within p succeeded */
        /* first pbuf q equals given pbuf */
        q = p;
        LWIP_DEBUGF(UDP_DEBUG, ("udp_send: added header in given pbuf %p\n", (void*)p));
    }
    LWIP_ASSERT("check that first pbuf can hold struct udp_hdr", (q->len >= sizeof(struct udp_hdr)));
    /* q now represents the packet to be sent */
    udphdr = (struct udp_hdr*)q->payload;
    udphdr->src = lwip_htons(pcb->local_port);
    udphdr->dest = lwip_htons(dst_port);
    /* in UDP, 0 checksum means 'no checksum' */
    udphdr->chksum = 0x0000;

    /* Multicast Loop? */
#if LWIP_MULTICAST_TX_OPTIONS
    if (((pcb->flags & UDP_FLAGS_MULTICAST_LOOP) != 0) && ip_addr_ismulticast(dst_ip))
    {
        q->flags |= PBUF_FLAG_MCASTLOOP;
    }
#endif /* LWIP_MULTICAST_TX_OPTIONS */

    LWIP_DEBUGF(UDP_DEBUG, ("udp_send: sending datagram of length %" U16_F "\n", q->tot_len));

#if LWIP_UDPLITE
    /* UDP Lite protocol? */
    if (pcb->flags & UDP_FLAGS_UDPLITE)
    {
        u16_t chklen, chklen_hdr;
        LWIP_DEBUGF(UDP_DEBUG, ("udp_send: UDP LITE packet length %" U16_F "\n", q->tot_len));
        /* set UDP message length in UDP header */
        chklen_hdr = chklen = pcb->chksum_len_tx;
        if ((chklen < sizeof(struct udp_hdr)) || (chklen > q->tot_len))
        {
            if (chklen != 0)
            {
                LWIP_DEBUGF(UDP_DEBUG, ("udp_send: UDP LITE pcb->chksum_len is illegal: %" U16_F "\n", chklen));
            }
            /* For UDP-Lite, checksum length of 0 means checksum
               over the complete packet. (See RFC 3828 chap. 3.1)
               At least the UDP-Lite header must be covered by the
               checksum, therefore, if chksum_len has an illegal
               value, we generate the checksum over the complete
               packet to be safe. */
            chklen_hdr = 0;
            chklen = q->tot_len;
        }
        udphdr->len = lwip_htons(chklen_hdr);
        /* calculate checksum */
#if CHECKSUM_GEN_UDP
        IF__NETIF_CHECKSUM_ENABLED(netif, NETIF_CHECKSUM_GEN_UDP)
        {
#if LWIP_CHECKSUM_ON_COPY
            if (have_chksum)
            {
                chklen = UDP_HLEN;
            }
#endif /* LWIP_CHECKSUM_ON_COPY */
            udphdr->chksum = ip_chksum_pseudo_partial(q, IP_PROTO_UDPLITE, q->tot_len, chklen, src_ip, dst_ip);
#if LWIP_CHECKSUM_ON_COPY
            if (have_chksum)
            {
                u32_t acc;
                acc = udphdr->chksum + (u16_t) ~(chksum);
                udphdr->chksum = FOLD_U32T(acc);
            }
#endif /* LWIP_CHECKSUM_ON_COPY */

            /* chksum zero must become 0xffff, as zero means 'no checksum' */
            if (udphdr->chksum == 0x0000)
            {
                udphdr->chksum = 0xffff;
            }
        }
#endif /* CHECKSUM_GEN_UDP */

        ip_proto = IP_PROTO_UDPLITE;
    }
    else
#endif /* LWIP_UDPLITE */
    {  /* UDP */
        LWIP_DEBUGF(UDP_DEBUG, ("udp_send: UDP packet length %" U16_F "\n", q->tot_len));
        udphdr->len = lwip_htons(q->tot_len);
        /* calculate checksum */
#if CHECKSUM_GEN_UDP
        IF__NETIF_CHECKSUM_ENABLED(netif, NETIF_CHECKSUM_GEN_UDP)
        {
            /* Checksum is mandatory over IPv6. */
            if (IP_IS_V6(dst_ip) || (pcb->flags & UDP_FLAGS_NOCHKSUM) == 0)
            {
                u16_t udpchksum;
#if LWIP_CHECKSUM_ON_COPY
                if (have_chksum)
                {
                    u32_t acc;
                    udpchksum = ip_chksum_pseudo_partial(q, IP_PROTO_UDP, q->tot_len, UDP_HLEN, src_ip, dst_ip);
                    acc = udpchksum + (u16_t) ~(chksum);
                    udpchksum = FOLD_U32T(acc);
                }
                else
#endif /* LWIP_CHECKSUM_ON_COPY */
                {
                    udpchksum = ip_chksum_pseudo(q, IP_PROTO_UDP, q->tot_len, src_ip, dst_ip);
                }

                /* chksum zero must become 0xffff, as zero means 'no checksum' */
                if (udpchksum == 0x0000)
                {
                    udpchksum = 0xffff;
                }
                udphdr->chksum = udpchksum;
            }
        }
#endif /* CHECKSUM_GEN_UDP */
        ip_proto = IP_PROTO_UDP;
    }

    /* Determine TTL to use */
#if LWIP_MULTICAST_TX_OPTIONS
    ttl = (ip_addr_ismulticast(dst_ip) ? udp_get_multicast_ttl(pcb) : pcb->ttl);
#else  /* LWIP_MULTICAST_TX_OPTIONS */
    ttl = pcb->ttl;
#endif /* LWIP_MULTICAST_TX_OPTIONS */

    LWIP_DEBUGF(UDP_DEBUG, ("udp_send: UDP checksum 0x%04" X16_F "\n", udphdr->chksum));
    LWIP_DEBUGF(UDP_DEBUG, ("udp_send: ip_output_if (,,,,0x%02" X16_F ",)\n", (u16_t)ip_proto));
    /* output to IP */
    NETIF_SET_HINTS(netif, &(pcb->netif_hints));
    err = ip_output_if_src(q, src_ip, dst_ip, ttl, pcb->tos, ip_proto, netif);
    NETIF_RESET_HINTS(netif);

    /* @todo: must this be increased even if error occurred? */
    MIB2_STATS_INC(mib2.udpoutdatagrams);

    /* did we chain a separate header pbuf earlier? */
    if (q != p)
    {
        /* free the header pbuf */
        pbuf_free(q);
        q = NULL;
        /* p is still referenced by the caller, and will live on */
    }

    UDP_STATS_INC(udp.xmit);
    return err;
}

/**
 * @ingroup udp_raw
 * Bind an UDP PCB.
 *
 * @param pcb UDP PCB to be bound with a local address ipaddr and port.
 * @param ipaddr local IP address to bind with. Use IP_ANY_TYPE to
 * bind to all local interfaces.
 * @param port local UDP port to bind with. Use 0 to automatically bind
 * to a random port between UDP_LOCAL_PORT_RANGE_START and
 * UDP_LOCAL_PORT_RANGE_END.
 *
 * ipaddr & port are expected to be in the same byte order as in the pcb.
 *
 * @return lwIP error code.
 * - ERR_OK. Successful. No error occurred.
 * - ERR_USE. The specified ipaddr and port are already bound to by
 * another UDP PCB.
 *
 * @see udp_disconnect()
 */
err_t udp_bind(struct udp_pcb* pcb, const ip_addr_t* ipaddr, u16_t port)
{
    struct udp_pcb* ipcb;
    u8_t rebind;
#if LWIP_IPV6 && LWIP_IPV6_SCOPES
    ip_addr_t zoned_ipaddr;
#endif /* LWIP_IPV6 && LWIP_IPV6_SCOPES */

    LWIP_ASSERT_CORE_LOCKED();

#if LWIP_IPV4
    /* Don't propagate NULL pointer (IPv4 ANY) to subsequent functions */
    if (ipaddr == NULL)
    {
        ipaddr = IP4_ADDR_ANY;
    }
#else  /* LWIP_IPV4 */
    LWIP_ERROR("udp_bind: invalid ipaddr", ipaddr != NULL, return ERR_ARG);
#endif /* LWIP_IPV4 */

    LWIP_ERROR("udp_bind: invalid pcb", pcb != NULL, return ERR_ARG);

    LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, ("udp_bind(ipaddr = "));
    ip_addr_debug_print(UDP_DEBUG | LWIP_DBG_TRACE, ipaddr);
    LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE, (", port = %" U16_F ")\n", port));

    rebind = 0;
    /* Check for double bind and rebind of the same pcb */
    for (ipcb = udp_pcbs; ipcb != NULL; ipcb = ipcb->next)
    {
        /* is this UDP PCB already on active list? */
        if (pcb == ipcb)
        {
            rebind = 1;
            break;
        }
    }

#if LWIP_IPV6 && LWIP_IPV6_SCOPES
    /* If the given IP address should have a zone but doesn't, assign one now.
     * This is legacy support: scope-aware callers should always provide properly
     * zoned source addresses. Do the zone selection before the address-in-use
     * check below; as such we have to make a temporary copy of the address. */
    if (IP_IS_V6(ipaddr) && ip6_addr_lacks_zone(ip_2_ip6(ipaddr), IP6_UNKNOWN))
    {
        ip_addr_copy(zoned_ipaddr, *ipaddr);
        ip6_addr_select_zone(ip_2_ip6(&zoned_ipaddr), ip_2_ip6(&zoned_ipaddr));
        ipaddr = &zoned_ipaddr;
    }
#endif /* LWIP_IPV6 && LWIP_IPV6_SCOPES */

    /* no port specified? */
    if (port == 0)
    {
        port = udp_new_port();
        if (port == 0)
        {
            /* no more ports available in local range */
            LWIP_DEBUGF(UDP_DEBUG, ("udp_bind: out of free UDP ports\n"));
            return ERR_USE;
        }
    }
    else
    {
        for (ipcb = udp_pcbs; ipcb != NULL; ipcb = ipcb->next)
        {
            if (pcb != ipcb)
            {
                /* By default, we don't allow to bind to a port that any other udp
                   PCB is already bound to, unless *all* PCBs with that port have tha
                   REUSEADDR flag set. */
#if SO_REUSE
                if (!ip_get_option(pcb, SOF_REUSEADDR) || !ip_get_option(ipcb, SOF_REUSEADDR))
#endif /* SO_REUSE */
                {
                    /* port matches that of PCB in list and REUSEADDR not set -> reject */
                    if ((ipcb->local_port == port) &&
                        /* IP address matches or any IP used? */
                        (ip_addr_cmp(&ipcb->local_ip, ipaddr) || ip_addr_isany(ipaddr)
                         || ip_addr_isany(&ipcb->local_ip)))
                    {
                        /* other PCB already binds to this local IP and port */
                        LWIP_DEBUGF(
                            UDP_DEBUG,
                            ("udp_bind: local port %" U16_F " already bound by another pcb\n", port));
                        return ERR_USE;
                    }
                }
            }
        }
    }

    ip_addr_set_ipaddr(&pcb->local_ip, ipaddr);

    pcb->local_port = port;
    mib2_udp_bind(pcb);
    /* pcb not active yet? */
    if (rebind == 0)
    {
        /* place the PCB on the active list if not already there */
        pcb->next = udp_pcbs;
        udp_pcbs = pcb;
    }
    LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("udp_bind: bound to "));
    ip_addr_debug_print_val(UDP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, pcb->local_ip);
    LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, (", port %" U16_F ")\n", pcb->local_port));
    return ERR_OK;
}

/**
 * @ingroup udp_raw
 * Bind an UDP PCB to a specific netif.
 * After calling this function, all packets received via this PCB
 * are guaranteed to have come in via the specified netif, and all
 * outgoing packets will go out via the specified netif.
 *
 * @param pcb UDP PCB to be bound.
 * @param netif netif to bind udp pcb to. Can be NULL.
 *
 * @see udp_disconnect()
 */
void udp_bind_netif(struct udp_pcb* pcb, const struct netif* netif)
{
    LWIP_ASSERT_CORE_LOCKED();

    if (netif != NULL)
    {
        pcb->netif_idx = netif_get_index(netif);
    }
    else
    {
        pcb->netif_idx = NETIF_NO_INDEX;
    }
}

/**
 * @ingroup udp_raw
 * Sets the remote end of the pcb. This function does not generate any
 * network traffic, but only sets the remote address of the pcb.
 *
 * @param pcb UDP PCB to be connected with remote address ipaddr and port.
 * @param ipaddr remote IP address to connect with.
 * @param port remote UDP port to connect with.
 *
 * @return lwIP error code
 *
 * ipaddr & port are expected to be in the same byte order as in the pcb.
 *
 * The udp pcb is bound to a random local port if not already bound.
 *
 * @see udp_disconnect()
 */
err_t udp_connect(struct udp_pcb* pcb, const ip_addr_t* ipaddr, u16_t port)
{
    struct udp_pcb* ipcb;

    LWIP_ASSERT_CORE_LOCKED();

    LWIP_ERROR("udp_connect: invalid pcb", pcb != NULL, return ERR_ARG);
    LWIP_ERROR("udp_connect: invalid ipaddr", ipaddr != NULL, return ERR_ARG);

    if (pcb->local_port == 0)
    {
        err_t err = udp_bind(pcb, &pcb->local_ip, pcb->local_port);
        if (err != ERR_OK)
        {
            return err;
        }
    }

    ip_addr_set_ipaddr(&pcb->remote_ip, ipaddr);
#if LWIP_IPV6 && LWIP_IPV6_SCOPES
    /* If the given IP address should have a zone but doesn't, assign one now,
     * using the bound address to make a more informed decision when possible. */
    if (IP_IS_V6(&pcb->remote_ip) && ip6_addr_lacks_zone(ip_2_ip6(&pcb->remote_ip), IP6_UNKNOWN))
    {
        ip6_addr_select_zone(ip_2_ip6(&pcb->remote_ip), ip_2_ip6(&pcb->local_ip));
    }
#endif /* LWIP_IPV6 && LWIP_IPV6_SCOPES */

    pcb->remote_port = port;
    pcb->flags |= UDP_FLAGS_CONNECTED;

    LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, ("udp_connect: connected to "));
    ip_addr_debug_print_val(UDP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, pcb->remote_ip);
    LWIP_DEBUGF(UDP_DEBUG | LWIP_DBG_TRACE | LWIP_DBG_STATE, (", port %" U16_F ")\n", pcb->remote_port));

    /* Insert UDP PCB into the list of active UDP PCBs. */
    for (ipcb = udp_pcbs; ipcb != NULL; ipcb = ipcb->next)
    {
        if (pcb == ipcb)
        {
            /* already on the list, just return */
            return ERR_OK;
        }
    }
    /* PCB not yet on the list, add PCB now */
    pcb->next = udp_pcbs;
    udp_pcbs = pcb;
    return ERR_OK;
}

/**
 * @ingroup udp_raw
 * Remove the remote end of the pcb. This function does not generate
 * any network traffic, but only removes the remote address of the pcb.
 *
 * @param pcb the udp pcb to disconnect.
 */
void udp_disconnect(struct udp_pcb* pcb)
{
    LWIP_ASSERT_CORE_LOCKED();

    LWIP_ERROR("udp_disconnect: invalid pcb", pcb != NULL, return);

    /* reset remote address association */
#if LWIP_IPV4 && LWIP_IPV6
    if (IP_IS_ANY_TYPE_VAL(pcb->local_ip))
    {
        ip_addr_copy(pcb->remote_ip, *IP_ANY_TYPE);
    }
    else
    {
#endif
        ip_addr_set_any(IP_IS_V6_VAL(pcb->remote_ip), &pcb->remote_ip);
#if LWIP_IPV4 && LWIP_IPV6
    }
#endif
    pcb->remote_port = 0;
    pcb->netif_idx = NETIF_NO_INDEX;
    /* mark PCB as unconnected */
    udp_clear_flags(pcb, UDP_FLAGS_CONNECTED);
}

/**
 * @ingroup udp_raw
 * Set a receive callback for a UDP PCB.
 * This callback will be called when receiving a datagram for the pcb.
 *
 * @param pcb the pcb for which to set the recv callback
 * @param recv function pointer of the callback function
 * @param recv_arg additional argument to pass to the callback function
 */
void udp_recv(struct udp_pcb* pcb, udp_recv_fn recv, void* recv_arg)
{
    LWIP_ASSERT_CORE_LOCKED();

    LWIP_ERROR("udp_recv: invalid pcb", pcb != NULL, return);

    /* remember recv() callback and user data */
    pcb->recv = recv;
    pcb->recv_arg = recv_arg;
}

/**
 * @ingroup udp_raw
 * Removes and deallocates the pcb.
 *
 * @param pcb UDP PCB to be removed. The PCB is removed from the list of
 * UDP PCB's and the data structure is freed from memory.
 *
 * @see udp_new()
 */
void udp_remove(struct udp_pcb* pcb)
{
    struct udp_pcb* pcb2;

    LWIP_ASSERT_CORE_LOCKED();

    LWIP_ERROR("udp_remove: invalid pcb", pcb != NULL, return);

    mib2_udp_unbind(pcb);
    /* pcb to be removed is first in list? */
    if (udp_pcbs == pcb)
    {
        /* make list start at 2nd pcb */
        udp_pcbs = udp_pcbs->next;
        /* pcb not 1st in list */
    }
    else
    {
        for (pcb2 = udp_pcbs; pcb2 != NULL; pcb2 = pcb2->next)
        {
            /* find pcb in udp_pcbs list */
            if (pcb2->next != NULL && pcb2->next == pcb)
            {
                /* remove pcb from list */
                pcb2->next = pcb->next;
                break;
            }
        }
    }
    memp_free(MEMP_UDP_PCB, pcb);
}

/**
 * @ingroup udp_raw
 * Creates a new UDP pcb which can be used for UDP communication. The
 * pcb is not active until it has either been bound to a local address
 * or connected to a remote address.
 *
 * @return The UDP PCB which was created. NULL if the PCB data structure
 * could not be allocated.
 *
 * @see udp_remove()
 */
struct udp_pcb* udp_new(void)
{
    struct udp_pcb* pcb;

    LWIP_ASSERT_CORE_LOCKED();

    pcb = (struct udp_pcb*)memp_malloc(MEMP_UDP_PCB);
    /* could allocate UDP PCB? */
    if (pcb != NULL)
    {
        /* UDP Lite: by initializing to all zeroes, chksum_len is set to 0
         * which means checksum is generated over the whole datagram per default
         * (recommended as default by RFC 3828). */
        /* initialize PCB to all zeroes */
        memset(pcb, 0, sizeof(struct udp_pcb));
        pcb->ttl = UDP_TTL;
#if LWIP_MULTICAST_TX_OPTIONS
        udp_set_multicast_ttl(pcb, UDP_TTL);
#endif /* LWIP_MULTICAST_TX_OPTIONS */
    }
    return pcb;
}

/**
 * @ingroup udp_raw
 * Create a UDP PCB for specific IP type.
 * The pcb is not active until it has either been bound to a local address
 * or connected to a remote address.
 *
 * @param type IP address type, see @ref lwip_ip_addr_type definitions.
 * If you want to listen to IPv4 and IPv6 (dual-stack) packets,
 * supply @ref IPADDR_TYPE_ANY as argument and bind to @ref IP_ANY_TYPE.
 * @return The UDP PCB which was created. NULL if the PCB data structure
 * could not be allocated.
 *
 * @see udp_remove()
 */
struct udp_pcb* udp_new_ip_type(u8_t type)
{
    struct udp_pcb* pcb;

    LWIP_ASSERT_CORE_LOCKED();

    pcb = udp_new();
#if LWIP_IPV4 && LWIP_IPV6
    if (pcb != NULL)
    {
        IP_SET_TYPE_VAL(pcb->local_ip, type);
        IP_SET_TYPE_VAL(pcb->remote_ip, type);
    }
#else
    LWIP_UNUSED_ARG(type);
#endif /* LWIP_IPV4 && LWIP_IPV6 */
    return pcb;
}

/** This function is called from netif.c when address is changed
 *
 * @param old_addr IP address of the netif before change
 * @param new_addr IP address of the netif after change
 */
void udp_netif_ip_addr_changed(const ip_addr_t* old_addr, const ip_addr_t* new_addr)
{
    struct udp_pcb* upcb;

    if (!ip_addr_isany(old_addr) && !ip_addr_isany(new_addr))
    {
        for (upcb = udp_pcbs; upcb != NULL; upcb = upcb->next)
        {
            /* PCB bound to current local interface address? */
            if (ip_addr_cmp(&upcb->local_ip, old_addr))
            {
                /* The PCB is bound to the old ipaddr and
                 * is set to bound to the new one instead */
                ip_addr_copy(upcb->local_ip, *new_addr);
            }
        }
    }
}

#if UDP_DEBUG
/**
 * Print UDP header information for debug purposes.
 *
 * @param udphdr pointer to the udp header in memory.
 */
void udp_debug_print(struct udp_hdr* udphdr)
{
    LWIP_DEBUGF(UDP_DEBUG, ("UDP header:\n"));
    LWIP_DEBUGF(UDP_DEBUG, ("+-------------------------------+\n"));
    LWIP_DEBUGF(
        UDP_DEBUG,
        ("|     %5" U16_F "     |     %5" U16_F "     | (src port, dest port)\n",
         lwip_ntohs(udphdr->src),
         lwip_ntohs(udphdr->dest)));
    LWIP_DEBUGF(UDP_DEBUG, ("+-------------------------------+\n"));
    LWIP_DEBUGF(
        UDP_DEBUG,
        ("|     %5" U16_F "     |     0x%04" X16_F "    | (len, chksum)\n",
         lwip_ntohs(udphdr->len),
         lwip_ntohs(udphdr->chksum)));
    LWIP_DEBUGF(UDP_DEBUG, ("+-------------------------------+\n"));
}
#endif /* UDP_DEBUG */

#endif /* LWIP_UDP */
